In the process for making brushes according to the prior art, the elements making up the brush are generally assembled using the threaded reduction device.
These components are, for the circular brushes, flanges, ring with wires and reduction device, and for the cup-shaped brushes, inner cup, ring with wires, outer cup and reduction device.
In the prior art methods, firstly the circular part of the reduction device is passed through the central hole present in the parts used for forming the brush, which are all obtained by cold moulding.
Secondly, there is a step for drawing an edge of the extension of the reduction device protruding beyond the elements which form the brush, whilst the other end of the reduction device has a larger dimension to prevent the escape of the elements.
The drawing produces a tab of the reduction device folded to secure together all the elements of the brush body (pressing them against the part of the reduction device with larger dimensions).
There is also, for the cup-shaped brushes, a retaining ring associated with an end portion of the outer cup and positioned outside the first portion of the of the wires for clamping them, exerting a pressure on them towards the inside of the brush, that is, towards the longitudinal axis (which also constitutes the axis of rotation of the brush when this is associated with a spindle).
This retaining ring is currently used, in the cup-shaped brushes, to have a better use of the metal wires.
It should be noted that the industrial brushes also differ according to the semi-worked element used, in which the wires are locked, and the material making the wires which must perform the brushing action.
With regard to the method of anchoring the wires to the flange, the semi-worked elements include twisted bundle rings and crimped or straight wire rings.
In the twisted bundle rings, the wires are grouped together in bundles, and screwed there by twisting; each bundle is associated with a hole formed by the flange close to its outer circumference.
In the crimped wire rings, the flange, which is called the ring nut, forms on a relative outer lateral edge a groove, in which the first portion (that is, the first end) of the wires is inserted.
The ring nut acts in conjunction with a supporting ring, about which the wires are then bent in a “U” shape, to keep the wires in the desired position.
The ring nut is also flanged to keep tight the wires bent and distributed along the entire circumference of the inner supporting ring (made of metal).
With regard to the material making up the wires, the brushes include metal wire brushes, plastic wire brushes, mixed metal-plastic wire brushes and natural wire brushes.
In this regard, it should be noted that the twisted bundle brushes always have metal wires. In other words, the twisted bundles configuration is not used for natural or plastic wire brushes. For this reason, the configuration with crimped or straight wire rings is always used for natural or plastic wire brushes.
The brushes must, for their use, be robust, in such a way as to work at particularly high speeds of rotation without breaking or deforming (in general, the mechanical parts from which they are made break or deform or the wires detach).
Another problem linked to the high speeds of rotation at which the brushes must operate consists in their stability and equilibrium.
The brush must always rotate as a rigid body about its longitudinal axis, which must remain stationary and without any movement from the axis of rotation during the working.
In addition, these must be the characteristics of all the types of brushes, therefore regardless of the materials with which the wires are made or the arrangement of the wires themselves or the system for production of the brushes and the elements used for their assembly (with metal elements obtained by cold moulding or with assembly of the various components with plastic materials).
The prior art deals with these problems by perfecting the finish and the assembly of all the elements which make up the brushes.
However, this results in an increase in the costs of the brushes, due to the number and the complexity of the components and their assembly.
In light of this, another drawback is associated with the fact of having numerous elements which make up the brush so that the brush production firms must hold a large supply of components in store (with a consequent waste of money, resources and space).
A further drawback of the prior art solutions, in terms of robustness and stability of the brush, consists in the machining tolerances of the components, especially of the reduction device and the parts which must be mounted with it for formation of the brush.
Another problem of the prior art solutions is linked to the fact that the brushes, made (for reasons of robustness) with components made of steel, must have increasingly large thicknesses with consequent increases in the costs and the problems in their production by cold moulding.
Lastly, the brushes comprising parts made of iron or plastic cannot be used safely for machining special metal surfaces (for example stainless steel), or in hazardous work environments which require explosion-proof safety measures, as there is the risk of producing sparks or electrostatic charges between the various components of the brush which in turn can produce electrostatic charges in environments with dangerous atmospheres due to the presence of gas.
It should be noted that there are technical solutions which involve welding together the wires of the brush with resins or adhesives, and then coupling a cap (that is, a cup) by pressure to the outside of the ends of the welded wires; the cup being made of plastic material, that is, obtained using special plastic resins or by embedding the wires or the rings with wires (semi-worked elements) in plastic dies.
These plastic caps or cups have a problem linked to the high fragility of the material, so they are only used with plastic wires in order to reduce the mechanical stresses.
This construction method cannot be used for the production of brushes with metal wires due to the high stresses and the high temperatures which are developed during their use.
Moreover, these solutions do not resolve the above-mentioned drawbacks, for example with regard to the possibility of using the brush in sterile environments, or with regard to the robustness and the resistance during operation at high speeds or at high temperatures, because the wires, which are welded and the outer plastic cup only acts as a covering element, detach or break.
Other more recent solutions use systems for the production of brushes with moulding by casting or by injection of the plastic material which, when solidifying, keep together all the components of the brush.
This latter production system, in particular with brushes with metal wires, also has the following main drawbacks:                there are many unbalanced brushes since the positioning in the mould of the wires or of the rings with wires is problematic;        the effect of the heating due to the increase in temperatures (approx. 100° C.) during the machining of the brush makes the mechanical strength of the plastic die which assembles the various elements of the brush critical.        
This drawback makes the breakage of the metal wires and, therefore, the break up of the brush easier, as the locking due to the plastic die quickly deteriorates with the increase in the temperature:                plastic cannot be used in the brushes with special metal elements (e.g. stainless steel or non-sparking) as it causes contamination of the surfaces or, as it is a plastic material, it can generate high differences in electrical potential between the various metal parts which make up the brush with the risk of electrical discharges (sparks);        different materials in the composition (plastic, steel, paints, etc) make the brush a very costly object for recycling.        